Within, for example, the printing and packaging industries, it is common practice to control working operations on a continuous material web by providing guide markings by means of printing on the web, these guide markings being sensed by photocells or other optical devices. These markings or control markings are often printed in a colour tone which makes a clear contrast with its surroundings, preferably black, and is applied on such panels or areas of the material web where no other printed markings or patterns occur. The markings may also be provided by means of magnetically sensible material or with the aid of mechanically sensible markings such as, for example, holes, crease lines or slots.
These guide markings are employed, for example, in the printing of multi-colour print, to adapt the position of the patterns printed with different colours to one another so that the different colour patterns will lie exactly superposed on one another. Another similar field of use is when the intention is, on a previously ready printed material web, to add print at a predetermined place in the print pattern, for example a best before date or the like or when the intention is to provide a printed pattern and a crease line pattern which facilitate fold forming, in register with each other.
Further fields of use are, for example, in those cases where the intention is, in a filling machine or the like, to advance a packaging material web an exact pattern length in order, on the one hand, to have the printed pattern in the same position on all packages, and, on the other hand, to cause the above mentioned crease line pattern to register with the forming devices of the filling machine so that the folding of the material takes place along the crease lines which are predetermined in position.
There is thus a need for an improved manner of determining a correct position for a further processing step to be performed to a packaging web.